260 Notes on the Biology of Pediculus humanus 
during the intervals, in a thermostat, preferably at 30° C. We have 
also raised them through their life-cycle on man making detailed 
observations on their biology. A full account of our investigations 
is in preparation for the press. 
G. H. F. N. 
On the Inheritance of Sex. 
The temperature of 30° C. was found to be the most satisfactory 
for rearing lice, and by feeding the insects twice a day large numbers 
were raised and maintained in the laboratory through five generations 
after which the experiment was stopped owing to the interruption 
caused by the war. In every case pairs of lice were isolated in glass 
tubes and kept separate so that the offspring of each pair could be 
raised separately. The results have been of great interest for they 
shew that in the louse the inheritance of sex is of a very peculiar type. 
The broods may be either of the following characters: 
(a) Entirely male. 
{b) „ female. 
(c) Male and female with the number of males predominating. 
{d) Male and female with the number of females predominating. 
Setting aside the various colour variations that were obtained the 
composition of some of the broods is shown below. 
First Series. 
Exp. 1. Broods from lice of unknown parentage. 
(a) Darkly pigmented $ x white (J; only 18 eggs were laid of which 
9 were reared to the adults. (Male brood.) 9^^ 
(o 1 ) The above cJ was crossed with another $; 17 eggs were laid but 
only 3 were reared to adult stage. (Mixed brood.) 1 1 $ 
( 6 ) Darkly pigmented x white $; 36 eggs laid, of which 17 
hatched and 12 became adult. (Male brood.) 12cJ<? 
(c) Dark c? x dark $; 23 eggs were laid of which 20 hatched and j 10 (JJ 
15 became adult. (Mixed brood.) ( 555 
(d) Dark ^ x dark 80 eggs were laid from which 35 nymphs 
natched and 26 became adult. (Male brood.) 
26 c?cJ 
